Process for manufacturing thermosetting resin particles

Abstract

Thermosetting resin particles having a narrow particle size distribution useful for powder coating application are produced by the steps of (a) providing a first water-soluble polymer having a cloud point within the range between 30 DEG C. and 90 DEG C. and a second water-soluble polymer not having any cloud point; (b) preparing an aqueous suspension in which an organic solvent-containing, liquid thermosetting resin composition is suspended as primary particles of oil droplets in an aqueous suspension medium containing the first and second water-soluble polymers, (c) heating the suspension to a temperature higher than the cloudy point to allow the oil droplets to agglomerate into secondary particles of larger particle sizes, (d) removing the organic solvent contained in the particles during or after step (c) and optionally (e) recovering the particles.

We claim: 
     
       1. A process for manufacturing thermosetting resin particles comprising (a) providing a first water-soluble polymer having a cloud point within the range between 30° C. and 90° C. and a second water-soluble polymer not having any cloud point;   (b) preparing an aqueous suspension containing said first and second water-soluble polymers and an organic solvent-containing, liquid thermosetting resin composition having a temperature of lower than the cloud point of said first water-soluble polymer, in which said resin composition is suspended as primary particles of oil droplets having a number average particle size of less than 10 microns;   (c) heating said suspension to a temperature higher than said cloud point to allow said primary particles to agglomerate and fuse into secondary particles having a number average particle size from 2 to 20 times greater than that of the primary particles; and   (d) distilling off the solvent from said secondary particles during or after step (c).   
     
     
       2. The process according to claim 1 further comprising recovering said secondary particles from the suspension. 
     
     
       3. The process according to claim 1 wherein the ratio of said polymer having a cloud point to said polymer not having cloud point is from 1:99 to 90:10 by weight. 
     
     
       4. The process according to claim 1 wherein said water-soluble polymer having a cloud point is polyvinyl alcohols having a degree of saponification of less than 85%, partly formalized polyvinyl alcohols, ethylene-vinyl alcohol copolymers, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol monoalkyl ethers, or ethylene oxide-propylene oxide block copolymers. 
     
     
       5. The process according to claim 1 wherein said water-soluble polymer not having cloud point is polyvinyl alcohols having a degree of saponification of greater than 85%, ethyl cellulose, hydroxyethyl cellulose or polyethylene glycols. 
     
     
       6. The process according to claim 1 wherein said organic solvent has a boiling point of lower than 100° C. or is removable by azeotropic distillation with water. 
     
     
       7. The process according to claim 1 wherein the concentration of said first and second water-soluble polymers in said aqueous suspension medium is from 0.02 to 20% by weight. 
     
     
       8. The process according to claim 1 wherein the final concentration of said liquid thermosetting resin composition in said suspension is from 10 to 50% by weight. 
     
     
       9. The process according to claim 1 wherein said liquid thermosetting resin composition comprises a binder resin and a crosslinker. 
     
     
       10. The process according to claim 9 wherein said binder resin is an epoxy, acrylic or polyester resin. 
     
     
       11. A powder coating composition comprising the thermosetting resin particles produced by the process of claim 9. 
     
     
       12. A powder coating composition comprising the thermosetting resin particles produced by the process of claim 10. 
     
     
       13. A process for the production of thermosetting resin particles, comprising heating an aqueous suspension of an organic solvent-containing, liquid thermosetting resin composition suspended as primary particles of oil droplets having a number average particle size of less than 10 μm in a dispersing medium containing a first water-soluble polymer having a cloud point of 30°-90° C. and a second water-soluble polymer not having any cloud point, from a temperature below to a temperature above the cloud point of the first water-soluble polymer, whereby the primary particles agglomerate and fuse into secondary particles having a number average particle size from 2 to 20 times greater than that of the primary particles. 
     
     
       14. A process according to claim 13, wherein the dispersing medium further contains a dye, a pigment, a UV absorber or an antioxidant. 
     
     
       15. A process according to claim 14, wherein the dispersing medium contains a pigment which is titanium dioxide, ferric oxide, yellow iron oxide, carbon black, phthalocyanine blue or quinacridon red. 
     
     
       16. A process according to claim 13, wherein the liquid thermosetting resin is a polyester, (meth)acrylate ester copolymer, aromatic vinyl compound copolymer, epoxy resin, phenol resin, melamine-formaldehyde resin or urea-formaldehyde resin. 
     
     
       17. A coated article, having thereon a coating composition of claim 11. 
     
     
       18. A coated article, having thereon a coating composition of claim 12.